A number of consumer electronic products use two conductors or two wires to communicate power from a power source to the appliance. Typically an electrical cord having two wires is connected to the appliance at one end and terminates in a two prong plug (one prong for each wire) at the other end. The two prong plug is then plugged into a power source, for example a power outlet or wall outlet. Consumer appliances such as kitchen appliances, televisions, stereos, and other consumer electronics are often "two-wire" appliances.
Other consumer electronic appliances are "three-wire" appliances. These three-wire appliances are connected to a power source, such as that provided by a wall outlet, using three-wires. Two of the three wires are connected between the power source and the appliance as they are for the two-wire appliance. The third wire is provided as a safety feature in order to dissipate an electrical hazard to ground. The third wire is variously referred to as the ground wire or the ground conductor. A computer system, such as that found in a home or office environment, is one example of a three-wire appliance. The chassis and metal enclosures for many three-wire appliances are coupled to the ground conductor in order to protect the consumer in the event that an electrical hazard is communicated to the chassis or the enclosure of the three-wire appliance. Ideally, any electrical hazard impressed upon the chassis or enclosure of a three-wire appliance will be diverted to ground through the ground conductor.
One manner in which an electrical hazard can be communicated to a two-wire or three-wire appliance is through a community antenna television (CATV) coaxial cable. CATV coaxial cables are commonly used to distribute radio frequency (RF) broadcast signals. Generally, any appliance that can be coupled to a CATV coaxial cable is a CATV device. The shield of the coaxial cable is typically connected to the chassis of the CATV device. Thus if the coaxial cable is exposed to an electrical hazard, the coaxial cable shield can communicate the hazard to the chassis of the CATV device. Furthermore, the possibility of exposure to the electrical hazard is increased if the chassis is electrically connected to a conductive enclosure of the CATV device.
A consumer can be exposed to a significant electrical hazard if the enclosure or chassis becomes energized due to an electrical hazard present on the shield of the CATV coaxial cable. For example, the CATV coaxial cable might come into contact with a power transmission line. Alternatively the CATV coaxial cable might be struck by lightning. Moreover, the hazard might be communicated to all CATV devices coupled to the CATV coaxial cable as well as any appliance coupled to any one of the CATV devices.
Electrical codes such as the National Electrical Code provide for the grounding of CATV coaxial cables near buildings in order to help minimize exposure to such hazards. (see, e.g., National Electrical Code, Art. 820 NFPA 70-1996). Unfortunately the codes do not ensure that the CATV coaxial cable has been grounded near the building or that the grounding is sufficient, especially if the building is a residential building (e.g., a single family dwelling).
Furthermore, although the ground conductor of a three-wire appliance is intended to dissipate electrical hazards, the ground conductor may not be properly or sufficiently grounded. For example, the three-wire appliance may not be plugged in at all (i.e., no ground connection). Alternatively, the three-wire plug may have been plugged into a two-wire socket (i.e., no ground connection) using an adapter plug. In another example, the ground conductor may be inadequately coupled to a ground so that the ground connection fails or is otherwise unable to fully dissipate the hazard.
Thus a method or apparatus for isolating community antenna television devices from an electrical hazard communicated on a community antenna television coaxial cable is needed.